The present invention relates to a fixed magnetic recording device, a method of adjusting a magnetic head, and a magnetic recording medium in electronic equipment.
In recent years, regarding a fixed magnetic recording device, a faster read/write characteristic has been required as a large recording density has been further demanded every year. A reproducing system needs a higher sensitivity to a magnetic flux than ever before. Currently, in many cases, a magnetoresistive head (MR head) is adopted, in which a reproducing output does not depend upon a peripheral speed of a magnetic recording medium. Namely, a head of a reproducing method using so-called magnetoresistance is adopted, in which an external magnetic field changes its electrical resistance. In the future, the trend is expected to shift to a GMR head, whose reproducing efficiency is improved by allowing a multilayer film to form a sensor for sensing a magnetic flux.
As the GMR head for practical use, a spin valve film head is applicable, in which a spin valve is used as a multilayer film serving as a magnetic sensing part. The GMR/inductive combined head is configured such that data is written using a conventional thin film head and data is read by using the GMR head, which is disposed next to the thin film head. Namely, the GMR head is used for only reading and is characterized by reducing the influence of the adjacent track when reading, because an obtained reproducing output is considerably larger than that of the thin film head, the reproducing output does not depend upon a peripheral speed of a magnetic disk, and a reading track width is smaller than that of the thin film head for writing. For this reason, the GMR head has been widely adopted as an HDD head. However, since the GMR head requires bias current according to its operating principle, it is necessary to prevent deformation on a waveform of a reproducing signal by optimally controlling bias current.
Incidentally, when the GMR head such as the above spin valve film head, which uses a multilayer film as a magnetic sensing part, is put into practical use, the most important challenge is to positively form single magnetic domains of NiFe, which forms a free-side magnetic film. If single magnetic domains are not formed on the free-side magnetic film, an external magnetic field causes variations on a waveform that is called Barkhausen noise, resulting in signal noise. When single magnetic domains are formed on the free-side magnetic film, Barkhausen noise is eliminated and preferable reproducing output can be obtained. As a method of forming single magnetic domains on a magnetic film, a method of disposing a magnetic domain control film on an end of a magnetic film is available. As for the magnetic domain control film, it is possible to use exchange coupling of an antiferromagnetic film and to form single magnetic domains by using a magnetic field (hard bias method) of a permanent magnet. Therefore, it is understood that materials and the configuration of the magnetic domain control film are the most significant for developing a spin valve film head.
However, in case of forming a head using a hard bias method, a magnet has been formed more precisely because a track pitch has been decreased every year. Thus, dispersion in lots is not ignorable that are resulted from difficult process control. Further, when the magnet is too strong, the GMR near the magnet is dead. However, once a permanent magnet is installed in a process of forming a thin film, modification cannot be made. Hence, under present circumstances, when an actual track width of a reproducing head is largely shifted from a design center at shipment inspection, the reproducing head is selected and discarded as a faulty component. Therefore, it is necessary to develop a technique for making fine adjustments on a track width.
The present invention is devised to solve the above problem. The object is to obtain a preferable reproducing output and to make fine adjustments on a track width when an actual track width is shifted from a design value, in a magnetic head using a hard bias system.
In order to solve the above problem, on a magnetic head including a multilayer film having a hard magnetic film (hard bias film) for adding a magnetic field on a magnetic resistant film in a longitudinal bias direction, the present invention further includes a solenoid on the hard bias film and controls the magnetic field in the longitudinal bias direction by means of current applied to the solenoid.
With this configuration, even when some dispersions are found on the hard bias film in a head process, it is possible to change the strength of the hard bias film by adjusting an amount of current applied to the solenoid, and an effective track width can be variable in size. Hence, it is possible to operate a reproducing head at a point having the best reproducing output on a magnetization curve or to adjust an effective track width even after manufacturing the reproducing head. Consequently, it is possible to improve a yield and to increase reliability of a drive by absorbing dispersions appearing when the head is manufactured. Further, linear responsiveness can be improved.
A magnetic recording device of the present invention, which includes a magnetic head using a hard bias system, the head having a hard bias film for adding a magnetic field to a magnetic resistance film in a longitudinal bias direction and for controlling a magnetic domain, is characterized in that the hard bias film includes a solenoid for adjusting the magnetic field running in a longitudinal bias direction. With this configuration, the magnetic field in a longitudinal bias direction can be kept at an optimum value. Thus, it is possible to improve linear responsiveness on a reproducing output of the magnetic head and to operate the magnetic head at a point having the best reproducing output on a magnetization curve. Therefore, even when the hard bias film has a dimensional deviation, the film being formed in a process of manufacturing the head, or in the event of dispersions in strength of a magnet, it is possible to bring the magnetic head to a stable operating point. Further, it is possible to adjust an effective track width of the magnetic head and to modify the effective track width in response to the influence of dispersions in size caused during manufacturing, a skew angle, a head flying height or the like.
Moreover, the present invention is characterized by further including a current generating circuit near the magnetic head to generate longitudinal bias current supplied to the solenoid. Thus, noise of reproducing output can be prevented.
Also, the present invention is characterized in that current control means for controlling longitudinal bias current supplied to the solenoid is used as a wiring pattern and is placed on a suspension of the magnetic head. Hence, a line for controlling longitudinal bias can be further provided.
Additionally, the current control means for controlling longitudinal bias current supplied to the solenoid is characterized by including a measuring section for measuring an effective track width of the magnetic head, a computing and determining section which computes a difference between a design value and a measured value and determines a current value based on the computation result, and a current adjusting section for adjusting current supplied to the solenoid in such a manner as to obtain a value determined by the computing and determining section.
A method of adjusting the magnetic head of the present invention is such that the magnetic head of a hard bias system having a hard bias film for adding a magnetic field to a magnetic resistance film in a longitudinal bias direction and for controlling a magnetic domain, is characterized by controlling current supplied to the solenoid provided on the hard bias film so as to improve the linear responsiveness of the reproducing output of the magnetic head by means of a magnetic field appearing on the solenoid. With this configuration, it is possible to operate the magnetic head at a point having the best reproducing output on a magnetization curve.
Also, the present invention is characterized in that since control is exercised on the current supplied to the solenoid provided on the hard bias film, a reproducing inert region of the magnetic head is increased or decreased by means of a magnetic field appearing on the solenoid, and an effective track width is varied. With this configuration, it is possible to cancel dispersions in effective track width resulted from the influence of dispersions in size upon manufacturing, a skew angle, a head flying height, or the like. Thus, it is possible to eliminate defects on the head which are caused by a shift of the effective track width.
It is also possible to obtain a constant effective track width.
Further, the present invention is characterized in that an effective track width of the magnetic head is measured by measuring means, a current value supplied to the solenoid is determined by computing and determining means based on the measured value and a design value, and the current is controlled by the current adjusting section to obtain a determined current value.
A magnetic recording medium of the present invention is characterized by including executing means for performing a series of operations of measuring an effective track width of the magnetic head by means of the measuring means, determining a current value, which is supplied to the solenoid, by means of the computing and determining means based on a measured value and a design value, and controlling current by means of the current adjusting means to obtain a determined current value. With this configuration, when the magnetic head shifts to a desired track of the magnetic recording medium, the executing means is read out and the series of operations are carried out. Thus, the effective track width of the magnetic head is adjusted.